1. Field of Invention:
This invention relates to voltage variable dielectric (VVD) composites. Specifically, the present invention relates to metal/dielectric VVD composites.
2. Description of the Related Art
There are currently two classes of VVD composites. Both involve mixtures of VVD with other dielectric materials. The first is simply a random mixture of VVD with a low loss dielectric. The disadvantages of this structure are the very large dielectric constant (about 100) and large bias voltages (several thousand volts typically) required. The second is the so-called xe2x80x981-3 composite,xe2x80x99 which consists of an array of VVD rods or vias embedded in a dielectric medium. For further information see US Pat. No. 5,607,631. Low dielectric constants can be obtained, in principle, with this method, however there is no reduction in the voltage requirement and there is no proven method of producing the structure.
Use of dielectric/dielectric composites does not allow much design flexibility. It is not possible to tailor current materials for specific applications. For example the dielectric/dielectric composites cannot be designed to have a more effective dielectric tuneability (even over a narrow range of frequency) than the base VVD material.
Hence, a need remains in the art for a VVD composite with low dielectric constant and low bias voltage. Furthermore, this material should be readily producible with established micro machining and film deposition techniques.
The need in the art is addressed by the voltage variable composite structure of the present invention. This invention comprises:
a) a first layer of metal;
b) a second layer of low-loss dielectric material impregnated with an array of first metal vias:
c) a third layer of a voltage variable dielectric;
d) a fourth layer of metal capacitors;
e) a fifth layer of low-loss dielectric material impregnated with an array of second metal vias; and
f) a sixth layer of metal.
The inventive structure comprises a square lattice of unit cells of height H, width W and length L. The low loss dielectric material has a dielectric constant ∈substrate. The metal vias traverse the entire thickness of the low loss dielectric material. The voltage variable dielectric material has a dielectric constant ∈VVD and a thickness T. The capacitors have a width Wid and a gap G.
The first metal via is adjacent the first metal contact and the second metal via is joined to the second metal contact. The dimensions of the structure are selected to produce an effective dielectric constant ∈eff whose value is given approximately by the following formulae:
∈eff=∈substrate+Cap*H/(W*L)xe2x80x83xe2x80x83[1]
Cap=∈VVD*Wid*T/Gxe2x80x83xe2x80x83[2]
The invention is preferably produced by first impregnating a low-loss dielectric material with an array of metal vias and coating one surface with a layer of metal. This structure can be cut to produce the second and fifth layers. Then the bottom of the second layer is coated with the layer of voltage variable dielectric material followed by the layer of patterned metallic film. Finally the two subassemblies are connected with the layer of voltage variable dielectric in the middle so that said first metal vias are adjacent to the first metal contacts and the second metal vias connect to the second metal contacts.
The metal can be any good conductor such as copper, gold and silver. The voltage variable dielectric material is about 100 to 1000 nm in thickness and is preferably made from barium strontium titanate. The low loss dielectric material is preferably micromachinable using low cost techniques. Candidates include silicon, gallium arsenide (GaAs), and the photopatternable lithium silicate glass, made by the Japanese company, Hoyo, known as PEG-3.
This invention has low dielectric constant (about 10) and a bias voltage on the order of tens of volts. Furthermore, it is readily producible with established micro machining and film deposition techniques. This invention may be tuned by the application of an electrical voltage. By varying the geometry of the metal microstructures, the composite can be designed to perform in a manner that is optimized for various electronic applications. The principle difference between this composite and previous tunable composite is the incorporation of embedded metal microstructures.
The metal/dielectric composite may be used for a variety electronic phase tuning applications. With suitably low loss materials, it may be employed at frequencies ranging from MHz to several hundred GHz. It may be used for phase tuning in different guided wave structures including rectangular wave guide (single-and multi-mode) and parallel plate. There are a number of methods by which it may be used for electronic beam steering including: (1) as the active element(s) in a scanning feed; and (2) integrated directly into the radiating elements of an antenna. Examples of (2) include continuous transverse stub antennas and dielectric lens antennas.
The principle advantage of voltage variable dielectric based phase shifting devices is low cost. The major obstacles to widespread use of VVD devices are the very high dielectric constant and large bias voltage requirement of these materials (and of current composites incorporating VVDs). The metal/dielectric composite eliminates both of these problems.
The invention can be used for electronic beam steering for radar and communication applications. The main advantage of the technology is that it would provide the beam agility required for applications such as synthetic aperture radar mapping, ground and airborne moving target interrogation, and point to multi-point communication, without the high cost of conventional, transmit/receive (T/R) module based, beam steering techniques. The invention may prove to be particularly important at millimeter wave frequencies (Ka band and above), since T/R module technology is underdeveloped and extremely expensive at these frequencies. Military systems that would benefit from this technology include space-based radar, unmanned aerial vehicles, and radar guided missiles. Commercial applications include point to multi-point communication: both ground-to-ground and ground-to-satellite.